With the improvement of the use efficiency of various rolling tools, tool materials suitable for high-speed cutting such as high-speed cemented carbide blades have been gradually popularized and applied. For a long time, our company is still a blank in the field of high-speed turning and rolling, and the surface roughness is less than ra1 The rotary parts of 6 adopt the traditional grinding or polishing process. The production efficiency is low, the working environment of workers is poor, and the labor intensity is high. In particular, the grinding process still has problems such as high cost and complex tooling. Therefore, the high-speed cutting process test is carried out with appropriate parts and tools, which can effectively reduce the labor intensity and processing cost and improve the production efficiency while ensuring the surface processing quality of parts. Related reading: practical comparison of multi ball rolling head

1. Discussion on process technical scheme

The output of brake piston made of cast iron in our company is particularly large, and the surface roughness of two outer circles of the parts is required to be Ra0 8. In the past, the process flow of "rough turning parts → semi-finished turning parts → grinding two outer circles → polishing chamfering" was used to complete the processing of the outer circle of parts. The surface roughness of the outer circle is not easy to ensure, and there are some problems, such as cumbersome processes, large impact on quality by human factors, dirty and poor working environment of workers, low production efficiency and so on.

Therefore, this paper studies the advanced turning technology of brake piston in order to improve the machining quality and efficiency, simplify the process flow and reduce the machining cost.

When machining the brake piston, a new turning process is used to directly turn the part to complete the finishing machining, that is, appropriate NC equipment, tooling and cutting tools are used to increase the finishing content after the original semi finishing process and cancel the original grinder processing process, which can not only ensure the surface quality of the part, effectively improve the processing efficiency, but also reduce the use of processing equipment and reduce the processing cost of the part. Therefore, the research of this technology is of great significance to the machining of rotary parts with high surface quality requirements.

2. Implementation of the scheme

2.1 process improvement

After learning the new processing technology and analyzing and studying the brake piston process, it is decided to select the NC lathe as the processing equipment, the fixture still uses the original semi-finished chuck, and the cutting tool adopts the machining tool or rolling tool of high-speed cutting.

The studied part brake piston is shown in Figure 1.

The parts are made of high-strength cast iron with a hardness of 200-220hb.

Original finishing process: grinding outer circles D1, D2 and D3, chamfering → polishing.

New processing technology: semi finish turning outer circle D1, D2, D3 and chamfer, leaving 0.1mm finish turning or rolling allowance → finish turning or rolling outer circle D1, D2, D3 and chamfer.

2.2 careful selection of tools

In step 1, a semi-finished cylindrical turning tool is used, and in step 2, a finished cylindrical turning tool or cylindrical rolling tool is used. After finishing, ensure the requirements of cylindrical size and roughness.

1) High speed turning process is used to finish machining. In the trial cutting, the cemented carbide blades of most tool manufacturers can meet the product quality requirements, but the service life of each blade is very different.

2) First, the high-speed turning process is used to complete the semi finishing, and then the rolling method is used to complete the finishing of the parts. In the trial cutting, the setting of rolling cutting parameters is very important. After carefully adjusting the cutting parameters, the rolling tools of various tool manufacturers can meet the machining quality requirements of parts. However, in practice, it is necessary to test repeatedly to find the cutting parameters suitable for the processed material.

Rolling processing is a plastic processing method to improve the surface roughness by rolling the roller with high hardness and smooth contact with the metal surface and making a small amount of plastic deformation on the surface layer. The surface roughness of the workpiece processed by rolling can reach ry0 in an instant 1-0.8, and the wear resistance is improved after the working surface is hardened, and the fatigue strength is also increased by 30%. The selection of rolling process parameters is very important: the size of rolling allowance determines the required rolling pressure, and the rolling pressure directly affects the rolling effect. If the rolling allowance is too large, the rolling cutter will wear rapidly, resulting in the decline of workpiece surface quality; If the rolling allowance is too small, the expected machining purpose cannot be achieved. Therefore, the minimum rolling allowance shall be selected as far as possible on the premise of ensuring the rolling accuracy. Before processing, test rolling shall be carried out for specimens of the same material and size to determine the best rolling parameters. For the piston studied in this paper, the rolling effect is the best when the rotating speed is 400R / min, the feed speed is 0.1mm/r and the rolling allowance is 0.05mm.